More problems, more money: Identifying and predicting high-cost rescue after colorectal surgery

Background Successful rescue after elective surgery is associated with increased healthcare costs, but costs vary widely. Treating all rescue events the same may overlook targeted opportunities for improvement. The purpose of this study was to predict high-cost rescue after elective colorectal surgery. Methods We identified adult patients in the National Inpatient Sample (2016–2021) who underwent elective colectomy or proctectomy. Rescued patients were defined as those who underwent additional major procedures. Three groups were stratified: 1) uneventful recovery; 2) Low-cost rescue; 3) High-cost rescue. Multivariable Poisson regression was used to identify preoperative clinical predictors of high-cost versus low-cost rescue. Results We identified 448,590 elective surgeries, and rescued patients composed 4.8 %(21,635) of the total sample. The median increase in costs in rescued patients was $25,544(p < 0.001). Median total inpatient costs were $95,926 in the most expensive rescued versus $34,811 in the less expensive rescued versus $16,751 in the uneventfully discharged(p < 0.001). When comparing the secondary procedures between the less expensive and most expensive rescued groups, the most expensive had an increased proportion of reoperation (73.4 % versus 53.0 %,p < 0.001). When controlling for other factors and stratification by congestive heart failure due to an interaction effect, a reoperation was independently associated with high-cost rescue (RR with CHF = 3.29,95%CI:2.69–4.04; RR without CHF = 2.29,95%CI:1.97–2.67). Conclusions High-cost rescue after colorectal surgery is associated with disproportionately greater healthcare utilization and reoperation. For cost-conscious care, preemptive strategies that reduce reoperation-related complications can be prioritized.


Introduction
Complications are an unfortunate but unavoidable part of surgical practice.However, not all complications are equivalently consequential.While many complications can be quickly recognized and remedied, there are infrequent complications that can lead to further deterioration and ultimately chronic critical illness or death.In the last two decades, a new emphasis in the patient safety and surgical quality literature has emphasized the importance of this latter sequence events and the resilience of an institution to arrest this deterioration cascade as a quality metric."Failure to rescue," defined as mortality following a complication [1], is now commonplace in the surgical quality literature and an established healthcare quality indicator [2][3][4][5].
While rescue has secured its place as a quality measure, little is known regarding its role in healthcare value, or quality divided by costs.
Evidence from patient harm literature suggests that surgical complications are a major healthcare cost burden.Responding to adverse events is responsible for 15 % of total global healthcare expenditures; the greatest burden of healthcare associated adverse events includes many related to prolonged surgical care including healthcare-associated infections, venous thromboembolism, and pressure ulcers [6].On average, a single complication after colorectal surgery is estimated to double the costs of surgical care [7].
With regards to the costs of rescue itself, there are few published studies.The existing literature on rescue costs is confined to single payer studies for single surgery types [8,9].In colorectal surgery, there is no estimate for the cost of rescue, or a major complication with deterioration, in the literature.Accurate assessments of healthcare costs are essential for planning and prioritizing surgical quality initiatives as well as advancing the use of novel healthcare services research methods such as cost-effectiveness analysis [10,11].The purpose of this study was to estimate the cost of rescue and identify predictors of high-cost rescue using nationally collected all-payer administrative data.We hypothesized that highly comorbid patients and rescue requiring invasive procedural interventions would be the greatest drivers of high-cost rescue cases.This study objective and hypothesis are important for both contextualizing contemporary healthcare costs and identifying specific drivers of high resource utilization.

Materials & methods
The following methodology was reviewed by the Yale Institutional Review Board and deemed exempt due to nonidentifiable data in a publicly available dataset.

Data source and target population
We used the National Inpatient Sample (NIS) from 2016 to 2019 to identify all admissions for adult patients ≥18 years old with an elective colectomy or proctectomy (ICD-10-PCS codes beginning with 0DT[E-P, excluding J appendiceal procedures]) occurring within the first 48 h after admission ("index surgery"); non-elective and emergent admissions were excluded based on NIS structured variables.The 48-h cutoff was used to ensure non-elective cases were excluded by a second means.Admissions with missing values for patient age, sex, LOS, vital status, or total charges were additionally excluded (641 patients omitted from cost analysis; only 96 patients omitted from non-cost clinical outcomes).
The NIS is an all-payer database of inpatient admissions to US community hospitals and is part of the Healthcare Cost and Utilization Project (HCUP), sponsored by the Agency for Healthcare Research and Quality (AHRQ).The NIS database is built as a 20 % stratified random sample of all hospital discharges collected by participating states, which represented 97 % of the US population in 2019.Primary diagnosis, up to 34 secondary diagnoses, and up to 25 procedures from the same admission are reported using ICD-10-CM and ICD-10-PCS codes.The NIS contains approximately 7 million records each year, and the data can be weighted to provide national-level estimates [12].

Case definition
We defined patients who required rescue as those with an index surgery followed by additional administratively coded procedures (any ICD-10-PCS code beginning with "0") occurring in the days following the operation (each ICD-10-PCS code has its own corresponding relative date of service from admission).We argue that given the limitations of administrative data and the limited and misuse of diagnostic coding, this approach more accurately ascertains those patients with serious complications.Postoperative diagnostic codesthe alternative measure that has been used for rescueare more likely to be missed than procedure codes given their limited impact on hospital or provider billing, in contrast to procedure codes [13,14].
On preparatory work for this study, we noted a unique relationship between costs and rescue for patients who survived to discharge versus those who died.These two relationships were sufficiently distinct that combining these two outcomes into a single analysis of rescue and costs would lead to incomplete and potentially inaccurate conclusions.Patients who died during their inpatient admission were excluded and planned to be studied separately in the future.

Identification of reoperations
We defined our primary explanatory variable to be reoperation.Postindex day ICD-10-PCS procedure codes were grouped by CCSR categories [15], which were then reviewed by I.L. and K.S. using clinical judgement to identify those that most likely represented returns to an operating room versus ancillary procedures (e.g., critical care procedures and monitoring, endoscopic procedures).We reviewed and grouped all remaining CCSR procedure categories into other clinically appropriate summary categories (Supplemental Table 1).

Admission costs
The NIS provides total hospital charges and total costs of admission via the HCUP-supplied cost-to-charge ratio derived from Centers for Medicare and Medicaid Services cost reports."Costs" defined in this manner refer to estimated healthcare system payouts based on nationally reported fee schedules.All costs were adjusted for inflation to 2019 dollars using the Consumer Price Index inflation calculator [16].Among all rescued patients, admission cost percentiles were calculated; patients were dichotomized into those with "high-cost rescue" (costs at or above the 75th percentile [$67,077]) and those with "lower-cost rescue" (below the 75th percentile).

Additional variables of interest
To determine the primary admitting diagnosis, the ICD-10-CM codes in the primary diagnosis field were categorized by CCSR and then organized by I.L. and K.S. into 6 clinically meaningful groups.The surgical approach used for the index surgery was determined as either minimally invasive or open by ICD-10-PCS code.Minimally invasive surgeries were further delineated as robotic-versus laparoscopicassisted with the former designated by the presence of the ICD-10-PCS code beginning with 8E0Wxxx ("Robotic assisted procedure of the trunk region") on the same day as the index surgery; all other minimally invasive cases were assumed to be laparoscopic.
Patient comorbidities were identified using ICD-10-CM codes in the secondary diagnosis fields.As the diagnosis codes in NIS are not tied to specific dates during admission or have indicators for present on admission, only comorbid conditions that were unlikely to have developed during admission were chosen (i.e., chronic conditions) (see Supplemental Table 2 for codes).Likewise, secondary diagnoses were examined to identify potential complications that occurred for patients in need of rescue.ICD-10-CM code descriptions and CCSR categories for secondary diagnoses were reviewed by I.L. and K.S. and grouped into categories of complication types (Supplemental Table 2).

Statistical analysis
All analyses were appropriately weighted to produce national estimates.Demographic and clinical characteristics of rescued patients were summarized overall, by receipt of reoperation, and by high-versus lower-cost rescue.Distributions of categorical variables were compared across groups using Pearson's chi-square tests, while means were compared using t-tests and medians compared using weighted bivariable quantile regression.
Total cost of admission was calculated for all rescued patients, as well as for those with and without reoperation; cost was calculated and graphed against length of stay to further describe the distribution and variability in costs among rescued patients.
Weighted, multivariable Poisson regression was used to estimate the risk of high-cost rescue by reoperation status.Potential confounders for adjustment were selected through a theory-driven approach with consideration for a parsimonious model if the effect estimate of interest was not substantially changed by the addition or removal of a given covariate.Only covariates that were reasonably believed to fully precede a reoperation were considered.The covariates used included age categories, sex, race/ethnicity, procedure approach, primary diagnosis, hospital bed size, and hospital teaching status.Effect modification was evaluated by stepwise testing for significance of covariate interactions with the exposure of interest.

Sensitivity analysis
The effect of reoperation on cost group assignment was evaluated using both inverse probability weighting with regression adjustment (IPWRA) and propensity score matching with 1:1 nearest-neighbor matching.The IPWRA approach used the same covariates as the multivariable regression approach to model the outcome (high-versus lowcost rescue) and used a logistic model with the same covariates, as well as additional comorbidities, to predict reoperation status.The propensity score matching approach used the same covariates as the regression, as well as additional comorbidities, to model the propensity scores using a logit model.Standardized differences, balance plots, and tests for overidentification were used to evaluate covariate balance over the different treatment levels for both approaches.Time to reintervention as a covariate was modeled for less expensive versus more expensive rescued patients, and there was no difference.
All statistical analyses were performed using Stata 17.0 MP (Stata-Corp, College Station, TX).The reporting of findings is in accordance with guidelines established by the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) Statement.

Results
We identified 448,590 elective colectomies and proctectomies in the NIS 2016-2019 data.Rescued patients composed 4.8 % (21,635) of the total sample.Table 1 provides preoperative characteristics of patients who were uneventfully discharged versus rescued.For rescued patients, results are further stratified by the less expensive group versus the most expensive patients as defined above.The most clinically relevant differences between the three groups were the proportion with underlying major comorbidities and the index resection procedural approach.Any major comorbidity was present in 40.1 % in uneventfully discharged versus 50.8 % in less expensive rescued patients versus 60.6 % in the most expensive rescued patients (p < 0.001).Most notably, congestive heart failure was closely correlated with being in the most expensive rescued subgroup (15.5 % versus 8.8 % in less expensive rescued versus 4.0 % in uneventfully discharged, p < 0.001).An open approach was used among 45.3 % of uneventfully discharged patients and >60 % in rescued groups (p < 0.001).There were no additional clinically relevant differences between the less expensive and most expensive subgroups (Supplemental Table 3).
Postoperatively, the most expensive rescued patients had significant higher healthcare utilization (Table 2).Median lengths of stay were 26 days in the most expensive rescued versus 11 days in the less expensive rescued versus 4 in the uneventfully discharged (p < 0.001).They were disproportionately discharged to other than routine care (22.8 % in uneventfully discharged versus 84.4 %, p < 0.001).Median total inpatient costs were $95,926 in the most expensive rescued patients versus $34,811 in the less expensive rescued versus $16,751 in the uneventfully discharged (p < 0.001).The overall median cost for rescued patients was $42,295.Length of stay was associated with increased costs, but the variability dramatically increased with increased lengths of stay (Fig. 1).All of these differences were significant for three-way comparisons between all groups as well as two-way comparisons between rescued subgroups (Supplemental Table 4).
When comparing the secondary procedures between the less expensive and most expensive rescue groups (Table 3), the most expensive group had an increased proportion of patients undergoing a reoperation (73.4 % versus 53.0 %, p < 0.001).The most common procedures when returning to the operating room included diversion (19.1 %) of top ten most common), re-closure of the abdominal wall (15.1 %), and bowel resection (46.4 %) (Complete list, Supplemental Table 5).Among rescued patients, reoperation was associated with an increase in median total costs of $13,259 (p < 0.001).Complicationrelated secondary diagnoses were also more common in the most expensive rescued group with the greatest clinical differences being in the rate of localized infection (63.7 % versus 38.5 %, p < 0.001), sepsis (45.8 % versus 11.2 %, p < 0.001), and secondary end-organ injury (73.5 % versus 11.2 %, p < 0.001).
When controlling for other factors with multivariable Poisson regression and stratification by congestive heart failure due to an interaction effect noted in early analyses, a reoperation was independently associated with high-cost rescue (RR with CHF = 3.29, 95%CI: 2.69-4.04;RR without CHF = 2.29, 95%CI: 1.97-2.67).This finding was robust to sensitivity analyses that evaluated the sequence of multiple rescue procedures as well regression with and without causal inference matching methods.

Discussion
In this study, we used the weighted generalizable cohort of the National Inpatient Sample to evaluate predictors of total inpatient costs of rescue after elective colorectal resection.As expected, we found that rescue is associated with an increased median length of stay by over 7 days, triples the need for enhanced post-hospital care, and more than doubles the median cost of admission.Interestingly, we found that while comorbidities are associated with the occurrence rate of complications, most comorbidities are not substantial drivers for additional costs independent of the rescue event.Moreover, and unique to this study, we found that the subset of rescued patients with high inpatient costs are disproportionately higher.Rescued patients from the 75th percentile of total inpatient costs subgroup are associated with lengths of stay >5 times longer.This same subgroup incurs total inpatient costs almost 6 times higher than non-rescued patients.Although unable to be quantified in this data, a residual cost burden by proxy of their rescue was that only 5 % of uneventful discharges went to skilled nursing facilities versus 21 % of less expensive rescued and half of most expensive rescued patients.Most clinically relevant, reoperation appears to be a significant independent driver of higher cost rescue.
Rescue efforts after complications from surgery are an essential component of a functioning healthcare quality ecosystem [17], and efforts to maintain healthcare resilience should be promoted [5,18].However, one criticism of the rescue-as-quality paradigm has been that a potential distortion of quality measurement induced by the use of a failure-to-rescue metric is that high complication rates with albeit low mortality may be overly-tolerated [19,20].In addition, these interventions incur disproportionate greater use of healthcare resources, and the consequences of resource utilization after rescue is not well understood.
The existing literature has few studies that have examined the costs of rescue.Chen et al. reviewed Medicare payments following rescue scenarios in hepato-pancreato-bliary operations and found that rescue events contributed an additional $8840 to the index hospitalization [8,9].Pradarelli et al. similarly examined 30-day Medicare payments and found that index colectomy complications in patients discharged alive led to $33,934 in additional 30-day costs [21].Our own study findings align well with these findings with more routine rescue costs contributing $25,544 of additional inpatient hospital charges.Unique qualities of our approach include a definition of rescue that uses postindex surgery procedures rather than administratively reported complication diagnostic codes.We believe this approach more accurately ascertains patients with serious complications given the realworld vagaries of how diagnostic codes in the postoperative period are applied to surgical episodes of care.Specifically, coders are more likely to identify and bill post-index procedures performed than the lowimpact postoperative complications codes [13,14].

Implications for future work
Rescue events after colorectal surgery highlight important opportunities for and prioritization of quality improvement.Not all complications or adverse outcomes are created equal.For example, a wellrecognized limitation of some quality reporting is that easily measured but minimally impactful outcomes such as superficial surgical site infections are not patient-centered and may be overemphasized [22].Quantifying the healthcare economic impact of rescue helps better characterize resource utilization for adverse outcomes and where efforts for quality improvement should be directed.
Our findings highlight that from a cost-effectiveness perspective, reducing the risks of reoperation may need to be prioritized to reduce high-cost outliers of colorectal surgery.In the context of healthcare system decision-making, care interventions that increase the risk of reoperation may require a higher clinical benefit to offset the disproportionate system risks of a subsequent rescue-directed reoperation.
An example can be drawn from our group's prior work with venous thromboembolism (VTE) prophylaxis.Extended VTE prophylaxis has a small clinical risk of reoperation for bleeding and significant but small benefit of preventing late-occurring postoperative VTE [23,24].Although further study is required, the risk of bleeding with extended VTE prophylaxis may disproportionately weigh against its use.Given that extended VTE prophylaxis increases the risk of reoperation for bleeding -historically thought to be a mere marginal risk for the patient and a system's healthcare utilizationthis study's findings caution further consideration of a preventative practice with unintended cost consequences.In another example, the cost-effectiveness of regionalizing rectal cancer may also be further informed by these findings.If postoperative complications and rescue events are reduced with traveling to high volume centers as evidence suggests [25,26], the benefit of regionalizing care may be further leveraged because the reduction in healthcare utilization liability reduces the sequelae of high-cost rescue events.Conversely, our findings may suggest that prevention efforts for complications that are readily treatable without returns to the operating room may not be as detrimental to healthcare system resilience and resource use.Superficial surgical site infections, arrhythmias, and other non-surgical complications may be clinically important to correct for the individual patient but have a dramatically lower impact on the healthcare systems in which they occur.Our findings would support perioperative preventative practices that target returns to the operating room (e.g., enhanced bleeding control, anastomotic leak prevention).For example, the most cost-effective complication prevention interventions are likely prophylactic use of hemostatic agents and adjunctive intraoperative steps for preventing anastomotic leak rather than superficial surgical site infection efforts or cardiopulmonary postoperative monitoring.

Limitations
This study is not without limitations.All data analyzed derived from NIS, a nationally representative dataset with its underlying data originally used for administrative billing purposes.The data has routinely been reused for retrospective studies, but conclusions must acknowledge that the findings represent actual care rather than a randomized comparison between exposure groups.The dataset also does not link specific diagnosis codes with each procedure code to allow clinical interpretation of indications for operations.Use of the National Inpatient Sample is further limited by selection bias and specifically that something other than the need for a post-index surgical procedure is what led to patients' being heavy resource use inpatient admission.In addition, NIS is only able to capture hospital costs from an index admission.Patients discharged and readmitted who then required rescue events are missing from our reported findings; and care costs that remained disproportionately higher in the post-discharge setting are not captured.It is likely that the difference in resource use between our uneventfully discharged and rescued categories understate the total healthcare cost impact.These limitations should not impact our conclusions in a meaningful way.

Conclusions
High-cost rescue after colorectal surgery is associated with disproportionately greater healthcare utilization in terms of length of stay, discharge disposition, and total inpatient costs.Reoperation following index resection appears to be an independent driver of high-cost rescue.For cost-conscious care, preemptive strategies that focus on reducing reoperation-related postoperative complications may require further prioritization.

Fig. 1 .
Fig. 1.Comparison of length of stay relative to total inpatient costs (in U.S. dollars) for colorectal resection with in-hospital rescue in NIS 2016-2019.Patients denoted with open blue circles are the most expensive (75th percentile) by total inpatient cost, and the remainder are marked in red.The x-axis is length of stay, truncated to 100 days.The y-axis is total inpatient costs, truncated to $600,000.Truncation was performed for better visualization and only excluded 10 patients.(For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Table 1
Demographic and clinical characteristics of patients hospitalized for elective colorectal resection in NIS 2016-2019, by admission outcome.

Table 2
Healthcare utilization of patients hospitalized for elective colorectal resection in NIS 2016-2019, by admission outcome.
a Denominator is LOS + 1 to account for same-day discharges (LOS = 0).